Sensory input to cells of origin of uncrossed spinocerebellar tract located below Clarke's column in the cat

Abstract

1. Sensory inputs to and locations of uncrossed spinocerebellar tract neurones in the lower lumbar cord were studied in chloralose-anaesthetized cats. 2. Neurones with axons ascending in the ipsilateral thoracic funiculi and projecting to the cerebellum were found mainly dorsal to the central canal (laminae V and VI) in the L5-L6 segments, i.e. at levels caudal to Clarke's column. Axons considered to originate from these cells were located in the dorsal half of the lateral funiculus at the level of L2, intermingled with axons of the dorsal spinocerebellar tract originating at the levels of Clarke's column. 3. Synaptic actions of primary afferents on neurones with antidromic invasion following stimuli applied to ipsilateral thoracic funiculi or to the cerebellum were investigated using intracellular or extracellular recording in the caudal lumbar segments. 4. Monosynaptic excitatory effects were evoked by electrical stimulation of group I muscle afferents of the hindlimb ipsilateral to the cell body. The majority of neurones received monosynaptic excitation from two or more muscles, predominantly extensors. They were frequently co-excited by group Ia muscle spindle and group Ib tendon organ afferents. 5. Volleys in cutaneous afferents produced excitation with short central latencies. In addition to the monosynaptic and disynaptic excitation from low-threshold cutaneous afferents, there were indications of monosynaptic effects from slightly slower conducting fibres. The majority of these neurones also received monosynaptic excitation from group I muscle afferents. Neurones with cutaneous input tended to be located more dorsally compared with those responding only to muscle afferents. 6. Volleys in joint afferents produced monosynaptic excitatory postsynaptic potentials (EPSPs) in the neurones with EPSPs from group I or group I and cutaneous afferents. 7. Some neurones were disynaptically inhibited from group I muscle afferents. Convergence of monosynaptic group I excitation and disynaptic group I inhibition occurred in varieties of patterns. 8. Polysynaptic excitation, inhibition or mixed effects of both were evoked from ipsilateral cutaneous afferents and high-threshold muscle and joint afferents, whereas effects from the controlateral afferents were feeble.(ABSTRACT TRUNCATED AT 400 WORDS)